Metal roller conveyor for microwave ovens

ABSTRACT

A roller type conveyor for microwave ovens in which the rollers are individually driven by suitable drive external to the oven. Each roller is supported on a strong metal shaft and is itself made of conductive metal. A microwave short is provided to prevent leakage in the region of the passageway in the oven wall through which the shaft extends. A dual speed embodiment of the invention is also disclosed as well as a complete system for the treatment of extruded foam polymers.

United States Patent [1 1 Gerling [11] 3,772,491 Nov. 13, 1973 METALROLLER CONVEYOR FOR MICROWAVE OVENS 3,508,023 4/1970 Veda et a1.219/1055 Primary Examiner-J V. Truhe Assistant Examiner-Hugh D. JaegerAttorney-Paul D. Flehr et al.

[57] ABSTRACT A roller type conveyor for microwave ovens in which therollers are individually driven by suitable drive external to the oven.Each roller is supported on a strong metal shaft and is itself made ofconductive metal. A microwave short is provided to prevent leakage inthe region of the passageway in the oven wall through which the shaftextends. A dual speed embodiment of the invention is also disclosed aswell as a complete system for the treatment of extruded foam polymers.

12 Claims, 6 Drawing Figures Pmmmxnv 13 ms 3.772.491

sum 10F 4 Fig! PAIENIEB ROY 13 I875 SHEET 3EF 4 METAL ROLLER CONVEYORFOR MICROWAVE OVENS BACKGROUND OF THE INVENTION This invention relatesto conveyors for microwave ovens and more particularly to a beltlessconveyor using metal driven rollers.

Heretofore, microwave ovens have commonly been provided with belts orrollers for continuously transporting materials through the oven. Wherebelts or rollers are made of dielectric materials they becomecontaminated by the material being processed, as by sticking to thedielectric material or flaking off on it. Such spots of contaminationbecome excessively heated and cause hot spots and uneven heatdistribution in the product being processed. Such dielectric materialsare also insufficiently resistant to chemical attack and'lack sufficientstrength at high temperatures. Furthermore, the use of a belt conveyorcauses nonuniform heating at the location of support forthe belt. Also,belt conveyors are unable to accommodate significant changes indimension of certain materials during transition through the oven. Anexample is that of foamed elastomers where the raw extrudate is cured inthe oven and expands in all directions. Vertical drop systems have beenused in order to eliminate the'need for a supporting conveyor system,but such vertical systems have not been satisfactory due to the stretchof the material being processed under gravity and limitations on thevertical length of the treatment area. In addition, vertical systems arenot useful where the material being treated is in the form of discreetsegments as, for example, where the material is supplied in lengths asin the treatment of wood products. There is, therefore, a need for a newand improved conveyor system for use in microwave ovens.

It is an object of the present invention to provide am improved conveyorfor use in microwave ovens which will overcome the above limitations anddisadvantages.

A further object of the invention is to provide a conveyor of theabovecharacter utilizing metal. rollers adequately supported on strong metalshafts externally driven from the oven, suitable means being providedfor minimizing leakage of microwave energy from the oven.

Another object of the invention is to provide a conveyor of the abovecharacter in which the metal rollers are spaced apart at sufficientdistance that the product being treated is free of the influence ofdielectric or conductive materials causing perturbations of theeffective microwave field throughout the material.

Another object of the invention is to provide a conveyor of the abovecharacter which can accommodate physical change in the dimensions of aproduct as in the curing of foamed rubber tubing.

Another object of the invention is to provide a conveyor of the abovecharacter in which the conveyor system is durable, has high weightsupport capacity at high temperatures and which is not subject to theformation of hot spots from processed material flaking or rubbing ontothe conveyor parts.

Another object of the invention is to provide a conveyor system of theabove character which eliminates the need for replacement of belts androllers, the durability of the elements of the system being such thatreplacement is hardly if ever necessary.

The foregoing objects have been achieved by providing a conveyor systemutilizing a plurality of metal rollers supported on metal shaftsjournalled in a suitable manner within a microwave oven to form a linearconveyor array. Means are provided for forming plurality of spacedpassages through one wall of the oven for permitting the ends of theshafts to extend through that walL'Gear means are affixed to the end ofeach shaft exteriorly of the oven and are connected through suitablepulleys and chain means to a source of rotary motion by which each ofthe rollers is driven at a desired speed. Means are provided for forminga microwave capacitive shunt between the shaft and the adjacent wall inthe region of the passageway through which the shaft extends so as tominimize leakage of microwave energy from the oven.

In one embodiment of the invention particularly useful in the treatmentof material which expands during treatment, one form of the invention isutilized as a preheater and a second form of the invention is utilizedas a treatment oven. The preheater is arranged to sense the temperatureof the material,-as for example being delivered from an extrusion deviceto the treatment oven, the amount of applied microwave energy beingcontrolled by asuitable pyrometer so that the material supplied to thetreatment oven is maintained at a constant temperature regardless of theenergy content of the material as it is extruded. Once passed into themicrowave oven suitable means are provided for sensing the position ofthe point of curing and expansion of the material and for' controllingthe amount of applied microwave power-to maintain the point of expansionin a predetermined location. A first set of driven rollers is providedbefore the point of expansion and are ganged together for movement at apredetermined speed. A second set of driven rollers is provided afterthe point of expansion of the material and are likewise ganged togetherand driven at a higher speed to accommodate the increase in length ofthe material as it is cured at the point of expansion.

These and other features and objects of the invention will becomeapparent from the following description and claims when taken inconjunction with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of themicrowave oven constructed in accordance with the present invention andutilizing metallic driven rollers in accordance therewith.

t FIG. 2 is a cross sectional plan view taken along the lines 2-2 ofFIG. 1. I

FIG. 3 is an end view taken along lines 3--3 of FIG.

FIG. 4 is a cross sectional view taken along the lines of 4-4 of FIG. 1.

FIG. 5 is a cross sectional view taken along the lines 5-5 of FIG. 1.

FIG. 6 is a top plan viewshown schematically-of a tubing curing systemutilizingmicrowave ovens having driven roller metal conveyor systemsconstructed in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIGS.1 through 5, there is shown a microwave oven and metal driven rollerconveyor I constructed in accordance with the present invention andgenerally consists of a suitable microwave oven indicated at 10. Themicrowave oven is mounted on a suitable framework 12 which is providedwith raised subframes l4, 16 at each end for mounting input and exitroller systems 18, 20.

Microwave oven is of any suitable type and includes conductive walls onall sides for confining microwave energy therein. Input and outletaccess openings are provided at each end of the oven and consist, forexample, of circular wave guide sections 22, 24 dimensioned to beoperated beyond cutoff so as to attenuate and minimize any leakage ofmicrowave energy therefrom. Suitable power supplies not shown, modestirrers and other auxiliary equipment, which are conventional in themicrowave oven art, have been omitted from the drawings for the sake ofclarity.

Means are provided for supporting and moving matemetal rollers 30amounted on metal shafts 32a in a linear array as shown in FIG. 2.Referring now to FIG. 5,'

where one of the driven roller assemblies is shown in detail andincludes rails 34, 36 mounted along the operative length of the oven andsupported by the end walls thereof, the rails are L-shaped in section soas to provide a rigid mounting surface having a horizontal upper side38. Teflon bearing blocks 40, 42 in the form of elongate members aremounted to the upper sides 38 of the respective support rails and areprovided with spaced apart and aligned passages. One end 44 of eachshaft is wholly contained within the oven and terminates in block 40.The other end 46 extends through an opening in the rear wall of theoven, an intermediate portion being supported in block 42 interiorly ofand adjacent to the rear wall 48. Suitable spacers 50, 52 are mounted onthe shafts and secured thereto with set screws for establishing theposition of the shaft relative to the oven.

Driven metal roller 30 is affixed to each shaft with a set screw atapproximately its midpoint for rotation therewith. The roller may beprovided with an exterio antistick coating 54 such as Teflon.

A suitable ball bearing assembly 56 is mounted to the oven wall 48exteriorly thereof for absorbing thrust and radial load applied to theshaft 32 by means to be hereinafter described.

Since the shaft extends through an opening formed in the oven wall, itpresents a potential hazard as it could serve as a coaxial transmissionline for permitting leakage of microwave energy from the oven. Means isprovided for forming a microwave capacitive shunt connected to the shaftand to the adjacent wall interiorly of said oven to minimize microwaveleakage of energy from the oven. Such means comprises a first discshaped member or projection 60 made of conductive metal and fastened tothe interior wall of the oven. A second conductive member 62 is formedin the shape of a disc and attached for rotation with the shaft by a setscrew. Together the disc projection 60 on the wall and the disc member62 attached to the shaft are arranged to form a closely spaced gap 64.and thereby provide sufficient capacitive coupling from the shaft to thewall to serve as a shunt for microwave energy. Preferably a Teflon shimis interposed between the members 60 and 62 to prevent contacttherebetween and to assure a close coupled relation without friction orshorting. The shim may be made of any suitable antifriction dielectricmaterial, a disc of Teflon 1 mil thick having been found suitable. 7

Referring generally to FIGS. 1 through 5, there is shown a system forgauging the respective ones of the shafts together and for driving themat uniform speed, which consists of a plurality of sprockets 66 attachedto the respective ends of each of the shafts 32 and driven by suitablelink chain drive 68. The chain drive passes over each of the sprockets66 and under interposed idler sprockets 70 mounted exteriorly of theoven on the rear wall thereof. The chain drive is driven by a suitablemotor 72 and tensioned by adjustment of an idler sprocket 74 adjustablymounted in a slot 76 provided in the input conveyor framework.

Input and output conveyors l8 and 20 are provided with a plurality ofmetal driven rollers and shafts of similar construction to thosedescribed above in connection with the'interior of the oven, except thatthe need for means for providing electrical shunt in the form of discsis unnecessary and has been eliminated.

In operation the conveyor of the embodiment shown in FIGS. 1 through 5is extremely effective. As the material is conveyed through the oven,the microwave fields of the oven are substantially unperturbed in theregions between the rollers so'that the field is effective in uniformlyheating the material; whereas, belt conveyors perturb the fields at thepoint of support and thereby produce uneven heating during the entirepassage of the material through the oven. However, at the rollerssurface the electric field virtually vanishes due to the requirementthat the electric field component of an electromagnetic field vanishesat the surface of a conductor. Thus,'adjacent these points of supportthe microwave heating effect is momentarily diminished. Accordingly, anymaterial flaking or sticking to the roller is not excessively heated andthe hot spots of prior devices are eliminated. Furthermore, the leakageof microwave energy is substantially avoided by the use of the microwaveshunts employed upon the shafts. By using metal shafts and metal rollersthe physical strength, resistance to chemical attack, and durability ofthe all metal system is improved to a point where conveyor replacementcosts are substantially reduced.

Referring now to FIG. 6, there is shown schematically a tubing curingsystem utilizing microwave ovens having driven metal conveyorsconstructed in accordance with the present invention and adapted to aparticular application of treatment and curing of expanded foam rubbertubing. Thus, as shown there is provided a suitable extrusion apparatus80 having a torpedo 82 disposed at the opening thereof capable offorming a tubular shape, as for example of foamed rubber material 84which is to be subsequently cured and expanded into a final tubularconfiguration. The material discharged from the extruder generally has avariable heat content, the temperature thereof being a function of itsstiffness and the amount of energy required to form the extrusion aswell as its initial temperature on being fed into the extrusionapparatus. In order to avoid the necessity of variations in downstreamprocessing time and speed, it is preferable to provide a preheatermicrowave oven '86 including a conveyor 87 constructed in is applied toa control circuit 90 which is sensitive to the temperature sensing meansfor varying the amount of microwave energy applied to the oven tothereby stabilize the exit temperature.-

Means are provided for forming a microwave treatment oven 92 arranged toreceive material from the preheater and for curing the same. Thetreatment oven is provided with first and second sections 94, 96,containing separate driven roller conveyors 96, 98 substantially thesame as that shown in FIG. 1 and a drive means for driving each of thefirst and second driven roller conveyor sections at different speedscalculated to accept a change in the physical dimension and speed ofmovement of material passed through the treatment oven. As known, foamedrubber being cured expands both laterally in dimension and in length sothat the input stream through the point of expansion travels at a lowerrate of speed than the exit stream. The means for driving the first andsecond roller conveyor sections at different speeds may take any ofvarious forms. In a typical installation it is preferred to gang eachsection together with a link chain and to drive them throughindependently controllable variable speed motors 96a, 98a so that thespeed of operation of the stream can be precisely controlled. In certainapplications, it may be possible to provide sprockets with a smallernumber of teeth on the second section with both sections being gangedtogether on a common drive. In this way the second section speed will behigher than that of the first section. 7

Means are provided for establishing the existence and location of thepoint of curing of the material in the case of foamed rubber tubing.Such'means consists of a first sensing system for detecting theexistenceof processed material prior to significant physical change inthe material at a predetermined location in the first section of theoven and can comprise aligned upper and lower photoelectric cells 100,102 and lights positioned across the path'of the tubing such that theunexpanded tubing does not interrupt the light path to the photoelectriccells. A second sensing system is'positio'ned subsequently across thepath of the stream and is used to detect the existence of the physicaland dimensional change in the treated material in that location. Suchmeans comprise a second set of photocells and lights 104, 106 positionedacross the path of the processed material such that the second sensingmeans is blocked by the expanded material but is not blocked by materialprior to its expansion. Thus, movement of the location 108 of thedimensional change of the treated material toward the input end of thetreatment oven is sensed by blocking the first sensing means, whilemovement of the location of dimensional change of the processed materialtoward the outlet is sensed by an unblocking of the second sensingmeans. The output of the first and second sensing means is applied to acontrol circuit 108 which varies the amount of power supplied to thatsection of the treatment oven such that movement of the location ofcuring toward the input decreases the amount of power while movementtoward the output and actuating the second signal means increases theamount of power. In this way the duration of treatment time and thelocation of expansion of the material is stabilized within the treatmentoven. In addition, the point of location is stabilized with respect toeach of the driven roller conveyors which operate at differing speeds toaccommodate the speed change of material passing through.

Many applications and modifications of the driven roller conveyor systemof the present application will occur to those skilled in the art towhich the invention pertains. In certain applications it may be ofadvantage to drive each roller of the conveyor by independent means andsuch a capability is provided by the present invention. In applicationsas for example the curing and expansion of foamed rubbers the presentinvention provides unique advantages in that the speed of the processline can be stabilized to a fixed value and controlled by a feedbacksensing circuit to stabilize the thermal and curing treatmenttemperatures and transit temperatures of the material beingprocessed'Because of the inherent rapid variability of microwave fieldsvirtually no thermal lag is experienced in the system as set forthherein. The present invention may be used with a variety of materialsand is not limited to the curing of expanded foam rubber materials. Forexample, it is contemplated that many other heat treatment processes canutilize apparatus as set forth herein as, for example, in the curing andcooking of sausages or of insulation boards or other discreet pieces ofmaterial desired to be heated. In certain cases it would be desirable toadvance the exit speed of materials being processed to which thetreatment oven as set forth in the description of FIG. 6 is immediatelyapplicable. Accordingly, the scope of the present invention is not to betaken as limited by the specific disclosure set forth herein, except'aslimited by the accompanying claims.

I claim:

1. A microwave oven and conveyor apparatus comprising means forming amicrowave oven and including end walls having openings therein foradmitting movement of material through said oven, conveyor means forsupporting moving material through said oven comprising a plurality ofconductive metal rollers, a plurality of metal shaft means fornon-rotatably mounting said rollers in a linear array in which therollers are in spaced apart relation to each other and aligned forsupporting material being conveyed thereon, means forming'passa'gesthrough one wall of said oven for permitting one end of each of saidshafts-to extend through said wall, the other ends of said shaftsterminating within said oven, driven means mounted on the ends of saidshafts exterior to said oven, drive means for engaging said driven meansto drive said shafts and rollers, means forming a microwave oven,conveyor means for supporting moving material through said ovencomprising a plurality of conductive metal rollers, a plurality of metalshaft means for mounting said rollers, said metal shafts and rollerstogether forming a solid metallic conformation without openings therein,a pair of guide rails mountedin spaced apart relation on opposite sidesand adjacent the walls of the interior of said oven, hearing blockssupported on said guide rails for rotatably carrying said shafts so thatsaid rollers are aligned in a linear array and are spaced apart inrelation to each other, one of the ends of said support rods terminatingat one of said bearing blocks, the other of said ends passing throughsaid bearing blocks, means forming passages through the wall of saidoven adjacent said last named bearing block for permitting said ends ofsaid shafts to extend through said wall, driven means mounted on theends of said shafts exterior to said oven, drive means for engaging saiddriven means to drive said shafts and rollers, means mounted on saidshafts interiorly of said oven and adjacent each of said passages forforming a microwave capacitive shunt between the shaft and theimmediately adjacent portion of the wall of the inside of said oven tominimize leakage of microwave energy therefrom, said shunt comprising adisc non-rotatably mounted on saidshaft and constructed and arranged toextend radially away from and surrounding said shaft and to present aconductive surface having a closely spaced relationship to a portion ofthe adjacent wall of the oven..

2. Apparatus as in claim 1 in which said microwave shunt furtherincludes a conductive means forming a disc projection on said wall, saidwall disc projection having an area comparable to the disc secured tosaid shaft.

3. Apparatus as in claim 1 in which said microwave oven and conveyorapparatus includes a microwave source for supplying power to said ovenand further in Y which heat sensing means is positioned at the output ofsaid oven for detecting the exit temperature of material thereat, acontrol circuit sensitive to said temperature sensitive means forvarying the amount of microwave energy delivered to the oven from saidsource to thereby stabilize the exit temperature of material beingprocessed therethrough.

4. Apparatus as in claim 1, further including an antifriction shiminterposed between said first and second conductive means.

5. Apparatus as in claim 1, further including a means forming an axialand thrust load absorbing bearing mounted on the outside of said ovenwall to support said shaft means.

6. Apparatus as in claim 1, in which said drive means includescontinuous chain link, motor means for engaging said chain link to drivethe same, said chain link being connected to each of said sprockets inturn to drive the same at at least one predetermined speed.

7. Apparatus as in claim 1 in which said means for driving said shaftmeans includes means for driving certain of said shafts at a firstpredetermined and the remainder of said shafts at a speeddifferent fromsaid first shafts.

8. Apparatus as in claim 1 wherein the outer periphery of each roller iscontoured to the shape of the material being conveyed.

9. Apparatus as in claim 7 wherein the outer periphery of each roller isprovided with an antistick coating.

10. Apparatus as in claim 1, further including input and output conveyormeans for supporting and moving material into and out from said oven,comprising at least one input metal roller and one output metal roller,metal shaft means for supporting each of said rollers in alignment withsaid conveyor rollers within said oven, sprocket means attached to saidshaft means, means connecting said sprocket means to said drive means.

1 1. A microwave oven and conveyor apparatus comprising means forming amicrowave oven and including end walls having openings therein foradmitting move-,

ment of material through said capacitive shunt connected to each of saidshafts and adjacent the wall inside of said oven to minimize leakage ofmicrowave energy from said oven, said capacitive shunt including atleast a conductive means forming a disc extending radially away fromsaid shaft and generally in spaced parallel relation to said wall ofsaid oven and secured to said shaft for rotation therewith, said shaftand the proximate portion of said oven wall being constructed andarranged to provide a closely spaced gap extending radially away fromand surrounding said shaft.

12. Apparatus as in claim 3 in which said bearing blocks are adapted tosupport said shafts for rotational movement, and further including anaxial thrust bearing mounted exteriorly of said oven and connected tosaid support shaft thereat.

1. A microwave oven and conveyor apparatus comprising means forming amicrowave oven and including end walls having openings therein foradmitting movement of material through said oven, conveyor means forsupporting moving material through said oven comprising a plurality ofconductive metal rollers, a plurality of metal shaft means fornon-rotatably mounting said rollers in a linear array in which therollers are in sPaced apart relation to each other and aligned forsupporting material being conveyed thereon, means forming passagesthrough one wall of said oven for permitting one end of each of saidshafts to extend through said wall, the other ends of said shaftsterminating within said oven, driven means mounted on the ends of saidshafts exterior to said oven, drive means for engaging said driven meansto drive said shafts and rollers, means forming a microwave oven,conveyor means for supporting moving material through said ovencomprising a plurality of conductive metal rollers, a plurality of metalshaft means for mounting said rollers, said metal shafts and rollerstogether forming a solid metallic conformation without openings therein,a pair of guide rails mounted in spaced apart relation on opposite sidesand adjacent the walls of the interior of said oven, bearing blockssupported on said guide rails for rotatably carrying said shafts so thatsaid rollers are aligned in a linear array and are spaced apart inrelation to each other, one of the ends of said support rods terminatingat one of said bearing blocks, the other of said ends passing throughsaid bearing blocks, means forming passages through the wall of saidoven adjacent said last named bearing block for permitting said ends ofsaid shafts to extend through said wall, driven means mounted on theends of said shafts exterior to said oven, drive means for engaging saiddriven means to drive said shafts and rollers, means mounted on saidshafts interiorly of said oven and adjacent each of said passages forforming a microwave capacitive shunt between the shaft and theimmediately adjacent portion of the wall of the inside of said oven tominimize leakage of microwave energy therefrom, said shunt comprising adisc nonrotatably mounted on said shaft and constructed and arranged toextend radially away from and surrounding said shaft and to present aconductive surface having a closely spaced relationship to a portion ofthe adjacent wall of the oven.
 2. Apparatus as in claim 1 in which saidmicrowave shunt further includes a conductive means forming a discprojection on said wall, said wall disc projection having an areacomparable to the disc secured to said shaft.
 3. Apparatus as in claim 1in which said microwave oven and conveyor apparatus includes a microwavesource for supplying power to said oven and further in which heatsensing means is positioned at the output of said oven for detecting theexit temperature of material thereat, a control circuit sensitive tosaid temperature sensitive means for varying the amount of microwaveenergy delivered to the oven from said source to thereby stabilize theexit temperature of material being processed therethrough.
 4. Apparatusas in claim 1, further including an anti-friction shim interposedbetween said first and second conductive means.
 5. Apparatus as in claim1, further including a means forming an axial and thrust load absorbingbearing mounted on the outside of said oven wall to support said shaftmeans.
 6. Apparatus as in claim 1, in which said drive means includescontinuous chain link, motor means for engaging said chain link to drivethe same, said chain link being connected to each of said sprockets inturn to drive the same at at least one predetermined speed.
 7. Apparatusas in claim 1 in which said means for driving said shaft means includesmeans for driving certain of said shafts at a first predetermined andthe remainder of said shafts at a speed different from said firstshafts.
 8. Apparatus as in claim 1 wherein the outer periphery of eachroller is contoured to the shape of the material being conveyed. 9.Apparatus as in claim 7 wherein the outer periphery of each roller isprovided with an antistick coating.
 10. Apparatus as in claim 1, furtherincluding input and output conveyor means for supporting and movingmaterial into and out from said oven, comprising at least one inputmetal roller and one output metal roller, metal shaft means fOrsupporting each of said rollers in alignment with said conveyor rollerswithin said oven, sprocket means attached to said shaft means, meansconnecting said sprocket means to said drive means.
 11. A microwave ovenand conveyor apparatus comprising means forming a microwave oven andincluding end walls having openings therein for admitting movement ofmaterial through said capacitive shunt connected to each of said shaftsand adjacent the wall inside of said oven to minimize leakage ofmicrowave energy from said oven, said capacitive shunt including atleast a conductive means forming a disc extending radially away fromsaid shaft and generally in spaced parallel relation to said wall ofsaid oven and secured to said shaft for rotation therewith, said shaftand the proximate portion of said oven wall being constructed andarranged to provide a closely spaced gap extending radially away fromand surrounding said shaft.
 12. Apparatus as in claim 3 in which saidbearing blocks are adapted to support said shafts for rotationalmovement, and further including an axial thrust bearing mountedexteriorly of said oven and connected to said support shaft thereat.